Omni-azimuth guidance system



Allg' 21, 1951 G. B. Ll'rcHFoRD ET AL 2,564,703

OMNI-AZIMUTH GUIDANCE SY STEM 5 Sheets-Sheet l Filed Oct. 29, 194'? ATTORN EY Aug. 21, 1951 G. B. LITCHF'ORD ET AL OMNI-AZIMUTH GUIDANCE SYSTEMFiled Oct. 29, 1947 5 Sheets-Sheet 2 INVENTORS GEORGE B. L /TC/-FORDJOSEP/ LVA/IHN ATTORNEY Aug 21, 1951 G. B. LITCHFORD ET AL 2,564,703

y OMNI-AZIMUTH GUIDANCE SYSTEM Filed oct. 29, 1947 s sheets-sheet slNvl-:NTORS 650,765 B. L/Tcf/FORD JOSEPH L YM/N ATTO R N EY Patented ng.2i, E

OMNI-AMER GUIDANCE SYSTEM Application October 29, 1947, Serial No. 782,722

13 Claims.

The present invention is concerned with navigational and traic controlaids for movable craft,

ing of a radio receiver and a phase-comparison direction indicator, e.g. a phasemeter.

In such arrangements, azimuthal direction in terms of the azimuthbearing from the fixed station may be determined within. an angle of afew degrees if care is exercised in the design and construction of theVtransmitting equipment and craft-borne receiving equipment. However,such systems are not suiliciently accurate where very close tolerancerequirements must be met, as for example in air trafiic control formodern highspeed aircraft in congested air traiiic zones. Furthermore,obstacles vsuch as buildings or sharp irregularities in the terrainwithin a radius of a few miles from the fixed transmitting station havebeen found to cause appreciable angular errors in the directiondeterminations afforded with these prior art systems. These troubleshave been particularly noticeable where a large low-frequency xedantenna array such as an Adcock array was supplied withsuccessivelyvaried energy components for eiiecting verticalaxis rotationof a radiation pattern lobe.

An object of the present invention is to provide improved omni-azimuthdirection vreference apparatus.

A more specic object is to provide an omniazimuth direction referencesystem characterized by more precise angular indication than heretoforeobtainable with omni-azimuth systems of single-lobe radiation patterns,and of accuracy capabilities in high contrast to those of prior, lowfrequency systems.

Yet a further object is to provide an omniazimuth direction determiningsystem wherein tendencies toward introduction of azimuth indicationerrors due to the presence of electromagnetic wave reflecting buildingsor hills or other irregularities of the terrain in the neighborhood ofthe xed reference station are substantially eliminated.

The present invention pvercomes the above shortcomings of prioromni-azimuth systems by the arrangement of the transmitting antenna toprovide a rotating pattern characterized not only by a single-lobe orlimacon-like general form but also by a scalloped or multi-lingeredoutline superimposed thereon, and by transmission and reception of tworeference phase signals of integral frequency ratio. One of thereference signals has a period equal tothe period of rotation of thedirective pattern and the other has a period shorter than the period ofthe iirst, in the ratio of the number of lingers superimposed upon thegeneral shape of the lobe. In the craft-borne receiving equipment, thephases are compared both as to the long-period waves and as to theshortperiod waves introduced by the several ngers, and high azimuthalaccuracy is achieved as well as greatly reduced error due to obstaclesor irregular terrain. 'This accuracy and independence of terrain errorsis enhanced by reliance upon physical rotation of such parts of theantenna system as are instrumental in determining the azimuthal energydistribution pattern, and by controlling the vertical-plane energydistribution pattern in such a Way as to concentrate most of thetransmitted energy in angles of elevation above the horizontal.

Referring now to the drawings,

Figs. 1 and 2 are diagrams of an omni-azimuth transmitting station and acraft-borne receiving equipment according to the present invention;

Fig. 3 is a circuit diagram illustrating the phase shifter systememployed in the receiving equipment of Fig. 2;

Fig. 4 is a polar plot of the azimuthal intensity distribution patternradiated by the transmitting antenna in Fig. 1;'

Figs. 5, 6 and 7 are oblique, elevation and sectional views,respectively, .of an antenna unit suitable for generating .theazimuthalf pattern of Fig. 4; v

Fig. 8 is a diagram of a relay interconnection modication applicable toFig. 2; f

Fig. 9 is an elevation ofthe entire fixed-station antenna system, partsbeing broken away to show the construction thereof;

Fig. 10 is an enlarged view of a section of the lens incorporated in theantenna system of Fig.

v9; and

Fig. 11 is a vertical-plane directivity pattern resulting from the useof the antenna system of Fig. 9. 1

In theilxed transmitting vstation of Fig. 1, an oscillator andvfrequency multiplier unit IM is provided for supplying radio-frequencyexcitation power to a' radiofrequency amplifier |05 3 having its outputcircuit arranged to drive a frequency multiplier and radio frequencypower amplifier |01. 'I'he power amplifier |01 supplies output power toa rotatably supported antenna. system |09 arranged to be rotated at highspeed by a driving motor I e. g. at 1650,12.. P. M.

The transmitting antenna is illustrated in Fig. as constructed in ashape generally resembling a vertical-axis drum, and the details of thisantenna may be as shown in Figs. 5 7, for producing an azimuthal radiantenergy distribution pattern generally according to Fig. 4.

The rotatable transmitting antenna |03 is of such design as to providean azimuthal radiation pattern substantially as shown in Fig. 4. This`pattern is characterized by a scallop planof n fingers, where n ispreferably an-odd number, e. g. 1l. Such a pattern may be produced bythe use of a double arcuate dipole and reflector central antenna with aspecial n-flnger pattern fringe modifier, as shown in Figs. 5, 6 and'-7. Two arcuate doublet or dipole parts 404 and 400 are provided (seeespecially Fig. '1), each having one arcuate arm connected to the outersheath 403 of a coaxial feed line and the other arm connected to theinner conductor 403 of the coaxial line. These arcuate dipoles eachoccupy a 120 sector about the vertical axis of the system, at a radiusof approximately V4 wavelength. A conductive reflector plate 43s issupported on an arm extending back from the outer sheath 403, this platebeing spaced approximately V4 wavelength from the axis of the system andbeing positioned directly opposite the two arcuate dipoles. Thedimensions of the reflector plate. in terms of wavelength, may beapproximately V4 wavelength high by V2 wavelength wide. The central unitcomprising antenna elements 404, 400, and 403 produces a limaconpattern, the shape of which is indicated in dotted line 4| in Fig. 4.

These elements are positioned at the middle of a drum formed with upperand lower conductive plates 4| and 4 I 3, which serve together as a waveguide for guiding the energy from the lcentral unit to the peripheralaperture. Vertical staves or columns such as column 4I3 are provided fordistorting the fringe of the limacon-shaped pattern in such a manner asto provide the n scallops or fingers therearound for achievingfineand-coarse modulation frequency control features, the resultantazimuthal directivity pattern of unit |09 being as shown at 43 in Fig.4. These n vertical bars may be made of dielectric material or of asemi-conductor, as desired, since the fringing can be accomplished byany such elements as will cause regular alternations around a circularlocus of the phase velocity of energy emerging between the peripheriesof plates 4|| and 4| 3.

Returning now to Fig. l, two alternating voltage generators I I3 and I5are coupled to antenna |09 so that their rotors revolve in fixedrelation therewith. These generators may comprise permanently magnetizedrotors and cooperating stator output coils. Generator ||5 is providedwith a two-pole permanently magnetized rotor, while generator I I3 isprovided with a rotor characterized by n pairs of poles, or a statormade up of n dual-pole sections. Generator IIS produces output voltageat the frequency of rotation of antenna |09, while generator |I3produces output voltage of n times the frequency of rotation. For thispurpose, generator ||3 may if desired be a. simple generator geared tothe rotor of generator I5 through n ratio gears. The voltage fromgenerator ||3 provides a reference for comparison with the rotationfrequency modulation component due to the general iimacon-like shape ofthe antenna pattern, and the output voltage of generator ||3 provides aphase reference signal for phase comparison with the high frequencyamplitude modulation component observed in any azimuth direction due tothe n scallops around the fringe of the directional pattern.

These reference phase voltages from generators ||3 and |I3 are added andamplified in unit IIT, and impressed by frequency modulation upon asubcarrier signal generated in an oscillator unit ill. This frequencymodulated subcarrier signal is in turn supplied to the input terminalsof an amplitude modulator |2| coupled to unit |03 for introducingsubcarrier modulation into the output energy radiated through antenna|33.

'The subcarrier modulation arrangement described above is merelyillustrative of the arrangements which may be used for transmittingphase reference signals to the craft. Another way to accomplish thephase reference signal transmission is by frequency modulation of unit|3| according to the phase reference signal wave, as set forth in U. S.Patent 2.377.902 to M. Relson.

A receiving system and azimuth direction indicator for responding to thetransmitter of Fig.

, 1 is set forth in Fig. 2. A craft radio receiver |3| having awide-band detector output circuit is coupled to the input circuits ofthree bandpass filters |33, |33 and |31. The last of these filter units,filter |31 is designed to respond to the subcarrier output frequency ofsubcarrier generator ||3 (Fig. 1), for selecting the demodulationcomponent of the received signal which is due to the subcarriermodulation in the fixed station system. This selected demodulationsignal is supplied to an amplifier, limiter and discriminatorarrangement |33 of conventional design for frequency modulationreception, and this unit supplies at its output terminals thedemodulation components corresponding to the' voltages impressed bygenerators |I3 and ||3 (Fig. 1) on unit ||1. l

The demodulation output voltage from unit |33 is supplied to the inputcircuits of band-pass nlters I4I and'l43. Band-pass filters |33 and |4|are designed to pass voltage components of the frequency of the outputof generator ||3; and filters |33 and |43 are tuned to pass the antennarotation frequency, i. e., the frequency produced by generator III.

A servo system is provided for anguiarly positioning a directional charttable "|43 in indicator 33 generally according to the phase relationbetween the outputs of band-pass filters |33 'and |43 and preciselyaccording to the phase relations between the'output voltages ofband-pass filters |33 and |4|. This servo system inclues a servomotor|41 coupled through a gear train |43 to the vertical shaft |3| of therotary asimuthal direction table |43, and an amplifier |33 for sup-Flying reversible-polarity excitation power to the control voltage inputterminals of the motor |41.

A first variable transformer I3| is provided with its rotor connecteddirectly to the shaft |3| and a second variable transformer |33 iscoupled through gears |34 andv |33 to the shaft |3I, the gear ratiobeing equal to the factor n. variable transformers |3| and |33 are unitsof the telemetric type, for example Selsyns. The rotor windings of theseunits are connected to the output circuits of band-pass filters |43 and|4|, respectively, and their respective multi-compo- These nent outputcircuits are connected to fixed phase shift combining networks |65 and|61.. I

Fig. 3 shows a Selsyn unit 6| connected to fixed phase'shift circuits3|6 and 3|1 and coupled through these circuits to the summation circuitincluding resistor elements 32| and 324. Circuits 3|6, 3|1 and elements32| and 324 together comprise a unit asv indicated at |65 in Fig. 2.This diagram illustrates the circuit interconnections likewise typicalof phase shifter system |63, |61. Phase shifters 3|6 and 3|1 are phaseshifting networks designed to produce opposite phase shifts totaling 120phase difference, so that the voltages at terminals 3|8 and 3 9 (withreference to common terminal 320) are added as 120-separated componentsof relative magnitudes dependent upon the angular position of the knob325. These components are combined to produce a voltage across resistor324 representing a phase shifted version of the input alternatingvoltage shifted through an angle as represented by the pointer positionof the knob 325. Such a phase shifting interconnection as illustrated inFig. 3 is described and claimed in application Serial No. 729,852, J. E.Browder et al., led February 20, 1947, now Patent No. 2,528,525, andassigned to-the assignee of the present invention.

` amplier |53 and the arrangement of the phase Shifters |6|, |63 andcombining networks |65, |61 are such that the motor |41 is made tooperate in direction and extent las required to maintain the turntable|45 positioned in azirnuthal direction generally according to the phaserelation between the outputs of filters |35 and |43 and more preciselyaccording to the-phase relation between the outputs of filters |4| and|33.

When the angular position of the turntable |45 is in accord with thebearing of the craft from the fixed station, the signals supplied tophase detector |69 directly from band-pass filter |35 and through thephase shifter system |6I, |65 from band-pass filter |43 areapproximately in the phase relation for zero output from`unit |69, andhence the output of this unit is inappreciable. Furthermore, under theseconditions, the phase relation between the signal supplied directly fromband-pass filter |33 to phase detector |1| and the signal suppliedthrough the phase shifter system |63, |61 from band-pass filter |4|willA be such as to produce zero output of phase detector |1|.Accordingly, the motor |41 remains inactive, and therefore the turntable|45 remains angularly fixed, its angular orientation denoting thebearing of the craft as observed from the fixed station. With gradualvariations of craft bearing, as due to craft progress along a non-radialcourse, a small error voltage appears at the output circuit of phasedetector |1|, sufficient to cause motor |41 to rotate the :table |45gradually and retain it in the correct angular alignment.

In an instance of appreciable angular disparity between the indicateddirection momentarily presented by the direction table |45 and theactual azimuthal bearing of the craft from the fixed station. as at themoment when the apparatus is switched on, then the phase relationbetween the signal fed directly from band-pass filter |36 to phasedetector |69 and the signal supplied by band-pass filter |43 and shiftedin phase shifter system |6I, |66 will be such as to produce anappreciable voltage at the output terminals of phase detector |69. Thisvoltage is of such polarity as to cause the motor |41 to turn the table|46 in the direction to restore a condition of substantial angularaccord of table |46 with the azimuthai bearing of the craft.

Then, until the turntable |45 has been brought to the orientationexactly according to the bearing of the craft, the signal fed directlyfrom bandpassfilter |33 and that shifted through units |63 and |61 arein such phase ,relation that unit |1| provides an output signalcompelling motor |41 to continue driving the turntable |45 until theangular setting is the exact representation of craft bearing. In normaloperating conditions,

after the turntable |46 has once been brought into the proper angularposition, the signals from unit |1| continuously retain the turntable|45 in the correct angular orientation.

While the present system can be successfully operated with directaddition of the outputs of the phase detectors |69 and |1| in supplyingthe motor amplifier |53, it is preferable that the coupling arrangementsbetween the input circuits of the amplifier |53 and the output circuitsof units |69 and |1| be so arranged as to suppress or eliminate thecontribution from phase detector |1| and to emphasize the contributionfrom phase detector |69 when the output from unit |69 is appreciable dueto a very large angular disparity; and to suppress or shut out theoutput of phase detector |69 and carry through the output of phasedetector |1| when the angular position of turntable |45 is approximatelycorrect, as indicated by the decrease of the output voltage of phasedetector |69 to a very low value. In this way, the azimuthposition-representing apparatus can be made to be controlled preciselyaccording to the scallop modulation signal, substantially independentlyof the general pattern frequencycomponent, during such time asapproximate angular accord of the turntable prevails as indicated by theoutput from phase detector |69 remaining in a relatively low range.

For the above purpose, an illustrative coupling arrangement may employordinary resistors |11 and |19 connected in series with nonlinearresistors 8| and |83,`respectively, in the output circuits of the phasedetectors |69 and |1|, the control voltage for amplifier |53 being madeup as the sum of the voltage drops across resistor |11 and nonlinearresistor |83. Nonlinear resistors |8| and |83 are illustrated as beingof the copper oxide rectifier type, each comprising a pair of oppositelyconnected rectifier elements in order to avoid overall rectification andasymmetrical operation of the phase detector output circuits withrespect to the reversible-polarity motor control signals. 'Ihesenonlinear circuits |11, |8| and |19, |93 act substantially as a relayoperating according to the output strength of phase detector |69 tocause the output thereof to be connected to the input circuit ofamplifier |53 in place of the output circuit of phase detector |1| whendetector |69 provides excessive output voltage.

If preferred, a control circuit may be arranged for selecting theoutputof one of the phase detectors |00, |1| and excluding the otherentirely from exercising any influence on the operation of theservomotor |01. purpo is illustrated in Fig. 8 where a relay |10 isshown employed in the interconnections of elements |00, |1| and |03instead of the nonlinear circuits shown in Fig. 2.

The actuating coil of the relay |10 is connected across the outputcircuit of phase detector |00, and the armature is arranged as adoublethrow switch for selecting between the two phase detectors. Whenunit provides a substantial output voltage, the amature is pulleddownward, so that the input circuit of unit |00 is supplied solely bythis coarse control phase detector |00. When the resulting servooperation has brought the azimuth direction indicator approximately intothe proper direction, the output voltage of phase detector |00 is sodecreased that the armature is released to move up and substitutetheoutput circuit of phase detector |1| in full control of the amplifier|00 and servomowr |41. The servomotor |41 is thereby operated to thefurther extent to bring the azimuth direction indicator into perfectaccord with the craft direction and through the operation of the phaseshifters connected thereto, output of phase detector |1| is reduced tozero. During normal operation, the armature of relay remains in theupper position, and variations of the output of phase detector I1I sumceto retain the turntable |05 in the angular position representing thecraft bearing.

The use of the multi-fingered or scalloped fringe in the rotatedpattern, and the turntable operation according to the phase comparisonbetween the high amplitude modulation frequency and the correspondingphase reference modulation provide such tight control of the azimuthangle indicator carried by the craft as to minimize the effects ofirregular terrain on the indicated bearings. For still furtherindependence of ground reflections of the transmitted energy. andparticularly for provision ofextremely accurate heading indications inaircraft, the vertical-plane distribution pattern of the transmittedlenergy may be limited to low angles above the horizon, with very littleenergy being propagated downward to be renected up from the earth.

To attempt to extend the rotatable antenna unit into a structure ofgreat height for sharp vertical-plane directivity would be dimcult, andwould involve serious problemsdn making such a system dynamicallybalanced for high speed rotation. According to a further feature of thepresent invention, the sharp vertical-plane directivity is accomplishedwithout any vertical extension of the rotating unit, by a cylindricallens system which surrounds the rotating antenna unit |00 and remainsstationary. This permits the multi-fingered and vlimacon-like pattern tobe revolved according to the rotation of the vertically pivoted antennaunit, and affects only the vertical-plane energy distribution.

Buch a lens system is illustrated at 202 in Figs. 9 and 10. This lenssystem surrounding the rotatable antenna |00 provides a vertical-planedirectivity fpattem as illustrated at 200 in Fig. l1. The completeantenna system is shown in a vertical elevation view in Fig. 9, partsbeing broken away to provide a clearer view of the honeycombedconstruction of the cylindrical lens and also to show the position ofthe rotatable An arrangement for this antenna'unit in relation thereto,and a portion by a biconical horn 206, 208,l for concentrating theenergy from the rotatable antenna unit |00 toward the inner cylindricalboundary of the lens 202. Biconical horn 200, 200 preferably is madestationary, with slight clearance for freedom of rotation of unit |00.

The horizontal membranes of the lens 202 are vmade up as annularmetallic discs which may be `of' 5000 megacycles are as follows:

Outer diameter of coaxial line 003, 000

` inches..- Diameter of drum unit |00 do l0 Radius of the dipole arms-do A Spacing of the reflector from the axis to the Height of thereflector do.. 1/2

' Length of the reflector do- 1% Spacing between the upper and lowerdiscs of the rotating drum inches l 2 Height of the lens system feet--l5 Diameter of the lens system do 25 Location of the drum: approximatelycentral in the lens system.

Vertical spacing of the horizontal membranes vin the lens system -inches11/2 Angular spacing between radial vertical fins in the lens systemApprox. 7

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be vmadewithout departing from the scope thereof,

l not in a limiting sense.

Certain subject matter disclosed herein and particularly relating to theantenna portion is disclosed and claimed in application S. N. 204,580flied January 5, 1951.

What is claimed is:

l. Aradio navigation system comprising antenna means pivoted about avertical axis for radiating a scalloped or multi-fingered limaconlikeazimuthal energy distribution pattern, means for rotating said antennameans about said vertical axis, means coupled to said antenna means fortransmitting first and second reference phase signal modulations, saidfirst reference phase signal modulation having a frequency equal to thenumber of revolutions of Said antenna per second and said secondreference phase signal modulation having a frequency given by theproduct of said number of revolutions per second and thenumber offingers varound said scalloped pattern, craft borne means for receivingenergy from said rotating antenna and demodulating said energy toproduce first and second amplitude demodulation rcomponents at theantenna rotation frequency and theproduct therewith of a number offingers in said pattern respectively, craft borne means for detectingsaid first and second reference phase signal modulations, and

means coupled to both said craft borne means for utilizing azimuthbearing data according to the phase comparison between said firstamplitude modulation component and said first reierence phase signalmodulation and according to the phase comparison between said secondamplitude modulation component and said second reference phase signalmodulation.

2. A radio navigation system as defined in claim l, wherein saidlast-named means comprises a rotatable azimuth bearing indicator, aservomotor coupled thereto for turningsaid indicator, a rst phasedetector for producing an output voltage varying according to the phaserelation between said first amplitude modulation component and saidfirst reference phase signal modulation, a second phase detector forproducing an output voltagel varying according to the phase relationbetween said second amplitude modulation component and said secondreference phase signal modulation, rst and second phase shifter meanscoupled to said rotatable azimuth bearing indicator for introducing intoan input circuit of said first phase detector and an input circuit ofsaid second phase detector, respectively, phase shifts varying accordingto the angular position of said azimuth bearing indicator. and means forcontrolling said servomotor primarily according to the output of saidfirst phase detector to bring said azimuth bearing indicatorsubstantially to the angular position corresponding to the direction ofthe craft from said antenna means and for controlling said servomotorprimarily according to the output of said second phase detector tocomplete the angular positioning of said azimuth bearing indicatoraccording to the direction of the craft from said antenna means.

3. A radio navigation system as defined in claim l, wherein said antennameans comprises substantially horizontal upperY and lower conductiveplates vertically spaced apart, an antenna unit substantially centrallylocated between said plates for launching ultra-frequencyelectromagnetic waves for propagation radially outward between saidplates, and means for introducing phase front distortion in saidelectromagnetic waves vto produce a scalloped phase front thereof in theregion between the peripheries of said plates, whereby the azimuthaldirective pattern of the emergent energy is characterized by amulti-ngered outline.

4. An omni-azimuth ground station compris- A ing a transmitter forgenerating radio frequency energy, an antenna assembly coupled to saidtransmitter and characterized by a radiation pattern of uneven generalintensity distribution over a range of azimuthal directions and also bya multi-lingered or scalloped outline, means coupled to said antenna forcausing rotation of said radiation pattern at a regular rotation speed,and means for transmitting to craft in the vicinity of said groundstation reference phase signals including a rst component having aperiod equal to the period of rotation of said intensity distributionpattern and a second component having a frequency greater than thefrequency of said rst component by a factor equal to the number of saidfingers in the outline of the radiation pattern.

5. A high-precision omni-azimuthal bearing determining system comprisingmeans for transmitting radio energy in an azimuthal intensitydistribution pattern characterized by a general llmacon-like shape witha plurality of fingers extending outward around the fringe thereof,means coupled to said transmitting means for causing regular rotation ofsaid pattern about the vertical axis, whereby the time variations ofintensity thereof in a given direction appear as amplitude modulation ofa rotation frequency component and a higher frequency component offrequency equal to the product of rotation frequency and the number ofsaid ngers, and means coupled to said transmitting means fortransmitting third and fourth modulation components, said third andfourth modulation components being of frequencies equal respectively tosaid rotation frequency and said higher frequency, whereby any directionfrom said transmitting means is defined by the phase relations betweenthe low frequency modulation components supplemented by the phaserelation between the higher frequency modulation components.

6. Omni-azimuth apparatus for inclusion in a movable craft, comprisingradio receiving means for receiving directional reference radio signalsand providing rst demodulation signals of frequencies f and nfcorresponding to the modulation components resulting from rotation of ann-ngered and asymmetrical radiation pattern about a vertical axis,second demodulation means for providing reference phase signals offrequencies f and nf of phases independent of azimuth receivingdirections, azimuth bearing indicator means, and phase responsive meanscoupled to said azimuth bearing indicator means for actuating saidindicator means generally accord- .ing to the phase relation between thedemodulation signals of frequency j and for completing the actuation ofsaid azimuth bearing indicator means precisely according to the phaserelation between the demodulation signals of frequency nf.

7. A navigation radio receiving system comprising a direction indicator,servo means for actuating said indicator, means for receiving andamplitude demodulating scalloped-fringe pattern-modulation signals andseparating the lowand high-frequency demodulation components resultingtherefrom, means for4 detecting lowand high-frequency phase referencesignal components, and phase comparator means for controlling said servomeans according to phase comparisons between ysaid lowand high-frequencydemodulation components and said lowand high-frequency phase referencecomponents, respectively.

8. A navigation radio receiving `system as dened in claim '7, whereinsaid phase comparator means comprises a low-frequency phase shifter anda high-frequency phase shifter both coupled to said rotatable directionindicator for producing phase shifts proportional to the angulardisplacement thereof, and a low-frequency phase detector and ahigh-frequency phase detector each having two input circuits, saidreceiving and amplitude demodulating and component separating meansbeing coupled to one input circuit of each of said phase detectors andsaid means for detecting lowand high-frequency phase reference signalcomponents being coupled to the other input circuit of each of saidphase detectors, the coupling to one of the input circuits of saidlow-frequency phase detectors including said low-frequency phase shifterand the coupling to one input circuit of said highfrequency phasedetector including said highfrequency phase shifter, and the outputcircuits of said phase detectors being coupled to said SGI'VO means.

9. A navigation radio receivingl system as defined in claim 8 whereinsaid servo means comprises a reversible servo-motor coupled to saidrotatable direction indicator, and the coupling between the outputcircuits of said phase detectors and said motor includesamplitude-responsive means for selectively differentiating between therelative control contributions of said low-frequency phase detector andsaid highfrequency phase detector according to the strength of theoutput of said low-frequency phase detector.

10. An omni-azimuthal radio navigation transmitting system comprisingantenna means including a vertical-axis rotatable member for radiatingultra-high-frequency energy in a multifingered or multi-lobedazimuth-plane distribution pattern, rotator means coupled to saidrotatable member for turning said distribution pattern about saidvertical axis at a predetermined angular velocity whereby the fieldintensity at a point in the vicinity thereof is modulated betweenmaximum and minimum amplitudes during each revolution of said member .bya number of modulation cycles corresponding to the number of fingers insaid pattern, and means for transmitting phase reference modulation'signals having a modulation component of period equal to the period ofrotation of said member and another modulation component of periodcorresponding to the time interval for said member to turn through anangle equal to the angle between two successive fingers in said pattern.said antenna means further including ymeans in said rotatable member forproducing an asymmetrical characteristic in said radiation pattern forphase comparison with the modulation component of the rotation period.

11. A radio navigation system comprising antenna means pivoted about avertical axis for radiating a scalloped or multi-fingeredV limaconlikeazimuthal energy distribution pattern, means for rotating said antennameans about said vertical axis, cylindrical -stationary wave guidelens'means surrounding said pivoted antenna means coaxially therewithfor restricting the vertical-plane energy distribution in the.

radiation pattern thereof, means coupled to said antenna means fortransmittingv first and second reference phase signal modulation. saidrst reference phase signal modulation having afrequency equal to thenumber of revolutions of said antenna per second and said secondreference phase signal modulation having a frequency given by theproduct of said number of revolutions per second and the number offingers around said scalloped pattern, craft-borne means for receivingenergy from said rotating antenna and demodulatingsaid energy to producefirst and second amplitude demodulation components at the antennarotation frequency and the product therewith of a number of fingers insaid pattern, respectively, craft-borne means for detecting said firstand second reference phase signal modulations, and means coupled toiboth said craft-borne means for presenting azimuth bearing dataaccording to the phase comparison between said first amplitudemodulation component and said first reference phase signal modulationand according to the phase comparison between said scond amplitudemodulation component and said second reference phase signal modulation.

12. Omni-azimuth apparatus for inclusion in a movable craft, comprisingradio receiving means for receiving rdirectional reference radio signalsand providing first demodulation signals of freqncies f and nfcorresponding to the modulation components of an asymmetrical n-fingeredradiation pattern rotated about a vertical axis, second demodulationmeans for providing reference signals of frequencies f and nf, phaseresponsive means coupled to said demodulation means for providing coarsedirectional data according to the phase relation between thedemodulation signals of frequency f and for providing ne directionaldata according to the phase relation between demodulation signals `offrequency nf.

13. Receiving apparatus for use in a coarse and ne omni-azimuth radiobearing indicating system, including means for detecting and separatingcoarse and fine reference and directional phase signals carried assimultaneous modulations on a single carrier, direction indicator means,first phase detector means responsive to said coarse reference anddirectional phase signals to actuate said indicator means approximatelyaccording to the phase relation between said coarse signals, secondphase detector means responsive to said fine reference and directionalphase signals and adapted to actuate said indicator means preciselyaccording to the phase relationship between said fine signals, and meansresponsive to said first phase detector to couple said second phasedetector to said indicator means only upon substantial completion ofsaid actuation of said indicator means by said nrst phase detectormeans.

GEORGE B. LITCHFORD. JOSEPH LYMAN.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS

